Steroid and Gonadotropin Responses to Ergocryptine-Suppressed Prolactin Secretion in Hysterectomized, Pseudopregnant Hamsters*

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Abstract
The influence of ergocyrptine (ECR) on suppressing PRL [prolactin] secretion and on steroid and gonadotropin levels was investigated in hysterectomized, pseudopregnant (HS-PSP) hamsters. At 0900 h of day 8 of PSP, hamsters were injected s.c. with ethanol or 10-100 .mu.g ECR; hamsters were then either inspected daily for a postovulatory discharge (indicating termination of PSP) or decapitated on days 8 (controls only), 9, 10, or 11, and serum was saved for RIA [radioimmunoassay]. Ten micrograms of ECR affected neither serum PRL levels nor shortened the duration of PSP. Twenty-five micrograms or more of ECR altered serum PRL levels and shortened the duration of PSP to 12 days or less compared to approximately 16 days in control HS-PSP animals. Fifty or 100 .mu.g ECR lowered serum PRL concentrations and induced luteal regression, as evidenced by declining levels of serum progesterone (P). Apparently PRL is necessary for luteal P secretion on day 8 of HS-PSP and the serum PRL level can not be lowered without shortening the duration of PSP. Twenty-four hours after 100 .mu.g ECR on day 8, serum P levels were < 1 ng/ml and serum E2 levels increased significantly; whereas serum LH [luteinizing hormone] and FSH [follicle stimulating hormone] levels were unaffected. Interestingly, spontaneous ovulation occurred on either days 10 or 11 after 100-.mu.g ECR treatment on day 8. To determine the acute effects of ECR on hormone levels, HS-PSP hamsters were injected s.c. at 0900 h on day 8 with 100 .mu.g ECR or ethanol. Hamsters were then either decapitated at various times from 0 (controls only) to 24 h after injection or serially bled cardiac puncture 3.times. daily until a postovulatory discharge was observed. In the decapitated groups, the ethanol-treated hamsters showed a striking inverse relationship between serum PRL, FSH, and LH with the latter 2 hormones elevated during the light period and PRL elevated during the dark period. ECR-treated hamsters exhibited a decline in the serum concentration of P [progesterone] (but not luteal P) before abolishment of the single nocturnal peak of PRL. The decline in PRL was followed by a terminal decline in serum and luteal concentration of P. ECR did not alter the serum level of FSH; however, LH was higher than in controls 3 h after treatment and lower 12 and 15 h after treatment. These results suggest that ECR may interfere with ovarian P production directly, but that abolishment of the single nocturnal surge of PRL induces a terminal decline in luteal and serum P. Serum P levels of serially bled ECR-treated hamsters revealed that if P levels were greater than 4 ng/ml on the morning of day 9, then ovulation occurred on day 11. Conversely, serum P levels of 4 ng/ml or less on day 9 resulted in ovulation by day 10. After ECR treatment the decline in serum P may be causally related to the timing of onset of ovulation.